Cathode active material and non-aqueous electrolyte cell

ABSTRACT

There is provided a non-aqueous electrolyte cell having a high capacity and superior in cyclic characteristics. Specifically, there is provided a non-aqueous electrolyte cell including a cathode  2  containing a cathode/positive active material, an anode  3  containing an anode/negative active material and a non-aqueous electrolyte, wherein the cathode/positive active material contains a lithium nickel composite oxide represented by the general formula Li A Ni 1−Z M Z O 2 , where A is such that 0.95≦A&lt;1, Z is such that 0.01≦Z≦0.5 and M is at least one of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca and Sr.

BACKGROUND OF THE INVENTION

[0001] 2. Field of the Invention This invention relates to a cathodeactive material containing metal lithium composite oxides and to anon-aqueous electrolyte cell containing this cathode active material.

[0002] 2. Description of Related Art

[0003] In keeping pace with the progress in the electronic technology inrecent years, there is a pronounced tendency towards higher performance,reduction in size and portability of the electronic equipment, such thata demand is raised for a secondary cell having a high energy density asa driving power supply for these electronic equipment. In theseelectronic equipment, a nickel-cadmium secondary cell, a lead cell, anickel hydrogen cell and a non-aqueous electrolyte cell, exploiting thelithium doping/undoping reactions, or so-called lithium secondary cell,are used.

[0004] Of these secondary batteries, the lithium secondary cell has amerit that it has high cell voltage, a high energy density, only littleself-discharge and superior cyclic characteristics.

[0005] Currently, lithium cobalt composite oxides, having high dischargepotential and high energy density, are predominantly used as a cathodeactive material for a lithium secondary cell. However, cobalt, as astarting material, is scanty as natural resources and are not stable insupply in future. For this reason, it has been proposed to use, as acathode active material, a lithium/nickel composite oxide or a nickelmanganese composite oxide, employing nickel and manganese and which aremore inexpensive and abundant as natural resources.

[0006] With the lithium secondary batteries, containing the lithiumnickel composite oxide as the cathode active material, not only LiNiO₂,but also a lithium nickel composite oxide, in which the proportion oflithium is slightly made higher by slightly changing the lithium nickelmolar ratio, or a lithium nickel composite oxide, in which metalelements other than lithium and nickel are solid-dissolved in crystalstructure, are used as a cathode active material to increase the cellcapacity.

[0007] However, the capacity of the lithium secondary cell cannot beraised beyond a certain limit even if a lithium nickel composite oxidehaving a larger proportion of lithium is used as a cathode activematerial. Thus, it is demanded of the non-aqueous electrolyte cell,employing a lithium nickel composite oxide, to raise not only itscapacity but also its cyclic characteristics. However, with theconventional lithium nickel composite oxides, such as lithium nickelcomposite oxides, in which the proportion of lithium in theircomposition is larger, it has been difficult to achieve higher cycliccharacteristics and higher cell capacity.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to provide acathode active material which achieves a high cell capacity and superiorcyclic characteristics which were not possible to achieve with theconventional lithium nickel composite oxides. It is another object ofthe present invention to provide a non-aqueous electrolyte cell having ahigh capacity and superior cyclic characteristics.

[0009] For accomplishing the above objects, the present inventors haveconducted eager researches, and have found that, if a lithium nickelcomposite oxide, in which the lithium to nickel molar ratio is slightlychanged so that the proportion of lithium in the composition is madesmaller than that in the case of the conventional lithium nickelcomposite oxide, is used as a cathode active material, it is possible torealize a non-aqueous electrolyte cell having cell characteristics thatcould not be achieved with the use as the cathode active material of theconventional lithium nickel composite oxide having a higher lithiumratio in its composition.

[0010] The cathode active material according to the present inventionhas been completed based on the above-described information, and residesin cathode active material containing a lithium nickel composite oxiderepresented by the general formula Li_(A)Ni_(1−Z)M_(Z)O₂, where A issuch that 0.95≦A<1, Z is such that 0.01≦Z≦0.5 and M is at least one ofFe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca and Sr.

[0011] By employing the lithium nickel composite oxide, represented bythe general formula Li_(A)Ni_(1−Z)M_(Z)O₂, such a non-aqueouselectrolyte cell may be realized which is of high capacity and which issuperior in cyclic characteristics.

[0012] For accomplishing the above objects, the present inventors haveconducted eager researches, and have also found that, by employing, as acathode active material in a non-aqueous electrolyte cell, a lithiumnickel composite oxide, in which the lithium/nickel molar ratio in theconventional lithium nickel composite oxide is slightly changed so thatthe proportion of lithium is smaller, there may be provided anon-aqueous electrolyte cell having cell characteristics not achievedwith the use as the cathode active material of the conventional lithiumnickel composite oxide with a larger proportion of lithium.

[0013] The non-aqueous electrolyte cell according to the presentinvention has been completed based on the above-described information,and resides in a non-aqueous electrolyte cell including a cathodecontaining a positive active material, an anode containing ananode/negative active material, and a non-aqueous electrolyte, wherein acathode/positive active material contains a lithium nickel compositeoxide represented by the general formula Li_(A)Ni_(1−Z)M_(Z)O₂, where Ais such that 0.95≦A<1, Z is such that 0.01≦Z≦0.5 and M is at least oneof Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca and Sr.

[0014] The non-aqueous electrolyte cell according to the presentinvention, containing a lithium nickel composite oxide represented bythe general formula Li_(A)Ni_(1−z)M_(z)O₂, as cathode/positive activematerial, has a high capacity and superior cyclic characteristics. Thatis, the cathode/positive active material of the present invention givesa non-aqueous electrolyte cell having a high capacity and superiorcyclic characteristics.

[0015] Moreover, the non-aqueous electrolyte cell according to thepresent invention is more excellent in cyclic characteristics and higherin capacity than the conventional non-aqueous electrolyte cellcontaining a lithium nickel composite oxide having a larger proportionof lithium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a cross-sectional view showing an illustrative structureof a square-shaped non-aqueous electrolyte secondary cell.

[0017]FIG. 2 is a cross-sectional view showing an illustrative structureof the non-aqueous electrolyte secondary cell shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Referring to the drawings, preferred embodiments of the presentinvention will be explained in detail.

[0019] A non-aqueous electrolyte secondary cell 1, embodying the presentinvention, is a so-called lithium ion secondary cell, and is comprisedof an elliptically-shaped cell unit, housed in a cell can 5 as shown inFIGS. 1 and 2. The cell unit is comprised of a band-shaped cathode 2 anda band-shaped anode 3, laminated together with a separator 4 in-between,and which are coiled together in the longitudinal direction. Anon-aqueous electrolyte liquid is injected in the cell can 5. Theopening end of the cell can 5 is sealed with a cell lid 6.

[0020] A terminal pin 7 is connected to a cathode lead 8 led out fromthe cathode 2, while the cell can 5 is connected to an anode lead 9 ledout from the anode 3. Thus, in the non-aqueous electrolyte secondarycell 1, the cell can 5 and the terminal pin 7 operate as an anodeterminal and as a cathode terminal, respectively.

[0021] The cathode 2 is comprised of a layer of a cathode/positiveactive material, formed on a cathode current collector. The layer of thecathode/positive active material is formed by coating a cathode mixture,containing a cathode/positive active material, on a cathode currentcollector, and drying the resulting mass in situ.

[0022] The cathode 2 in the non-aqueous electrolyte secondary cell 1contains, as a cathode active material, a lithium nickel composite oxiderepresented by the general formula L1i_(A)Ni_(1−Z)M_(Z)O₂, where A issuch that 0.95≦A≦1, Z is such that 0.01≦Z≦0.5 and M is at least oneselected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga,Cr, V, Ti, Mg, Ca and Sr.

[0023] When a lithium nickel composite oxide is used as acathode/positive active material a lithium nickel composite oxide,having a larger proportion for lithium, such as a compound representedby the general formula Li_(A)Ni_(1−z)M_(Z)O₂, where A is 1 or more, hasso far been used. However, with the non-aqueous electrolyte secondarycell, containing, as the cathode/positive active material a lithiumnickel composite oxide, having a higher proportion for lithium, a demandhas been raised for improving cyclic characteristics, even though thecell has practically satisfactory cell capacity.

[0024] The present inventors have conducted eager searches and havearrived at the information that, by using, as a cathode/positive activematerial, a lithium nickel composite oxide having smaller lithiumcontents by slightly changing the lithium to nickel molar ratio, that isLi_(A)Ni_(1−Z)M_(Z)O₂, where A≦0.95≦1, such a non-aqueous electrolytesecondary cell 1 may be produced having cell characteristics notachievable with the use as the cathode/positive active material of theconventional lithium nickel composite oxide having a larger proportionfor lithium.

[0025] The non-aqueous electrolyte secondary cell 1, containingLi_(A)Ni_(1−Z)M_(Z)O₂, where 0.95≦A<1, as the cathode/positive activematerial, is of a high capacity, and is superior in cycliccharacteristics. It is noted that, although the range of A is optionallyselected within the above range, the above range of 0.95≦A<1 is moreappropriate in the perspective of raising the capacity of thenon-aqueous electrolyte secondary cell

[0026] It is noted that Li_(A)Ni¹⁻M_(Z)O₂, where 0.95≦A<1, may beobtained by using, as a starting material, carbonates, nitrates, oxidesor hydroxides of lithium, nickel and M in the above formula, mixingthese in amounts corresponding to the composition, specifically, so thata carbonate, a nitrate, an oxide or a hydroxide, for example, oflithium, is contained in the composition in a molar ratio of not lessthan 095 and less than 1, and on sintering the resulting mixture in atemperature range from 600° C. to 900° C.

[0027] As a cathode/positive active material to be used in combinationwith Li_(A)Ni_(1−Z)M_(Z)O₂, where 0.95≦A<1, lithium manganese compositeoxides, specifically the compounds represented by the general formulaLi_(x)Mn²⁻Y M'_(Y)O₄, where X is such that 0.9≦X,Y is such that0.01≦Y≦0.5 and M' is at least one of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V,Ti, Mg, Ca and Sr, may be used.

[0028] In particular, the non-aqueous electrolyte secondary cell 1,employing a lithium nickel composite oxide, represented by the generalformula Li_(A)Ni_(1−Z)M_(Z)O₂, where 0.95 ≦A<1, and the compoundrepresented by the general formula Li_(x)Mn_(2−Y)M'_(Y)O₄, incombination, is not only of a high capacity, but also is furtherimproved in cyclic characteristics and superior in safety.

[0029] In particular, in order to synthesize Li_(A)Ni_(1−X)M_(Z)O₂ ofhigh capacity and superior thermal stability, as a lithium nickelcomposite compound Li_(A)Ni_(1−A)X M_(Z)O₂, as the aforementionedcompound, a co-precipitated nickel cobalt hydroxide is first prepared.Specifically, a compound of nickel or cobalt of nitric acid or sulfuricacid, soluble in an aqueous solution, or a chloride of nickel or cobalt,are co-precipitated by a reaction of neutralization, using, for example,a basic solution of alkali metals.

[0030] This co-precipitated hydroxide is obtained by dissolving e.g.,nickel sulfate and cobalt sulfate at a preset ratio and mixing asolution of sodium hydroxide in the resulting solution.

[0031] This co-precipitated hydroxide is then dried and added to with analuminum compound at a preset ratio. The resulting product then isstirred and mixed together. To the resulting mixture, lithium hydroxideis added at a preset ratio, stirred and mixed together to yield aprecursor of Li_(A)Ni_(1−B−)Z Co_(B)Al_(Z)O₂.

[0032] As an aluminum compound, such a compound having an averageparticle size of 10 μm or less is preferred. By setting the averageparticle size to 10 μm or less, aluminum can be sufficientlysolid-dissolved in the subsequent sintering step to assure optimumreactivity. When the average particle size exceeds 10 μm, soliddissolution of aluminum is insufficient such that impurities areproduced along with Li_(A)Ni_(1−B−)Z Co_(B)Al_(Z)O₂. Specified examplesof aluminum compounds may include aluminum hydroxide, aluminum oxide(alumina), aluminum nitrate, aluminum sulfate, and aluminum chloride.However, in consideration that decomposed gases may be evolved duringsintering, aluminum hydroxide or aluminum oxide is preferably used as analuminum compound. In particular, by using aluminum oxide with anextremely small average particle size, as the aluminum compound,Li_(A)Ni_(1−B−Z)Co_(B)Al_(Z)O₂ of superior quality may be produced.

[0033] Although the mixing ratio of the lithium nickel composite oxide,represented by the general formula Li_(A)Ni_(1−Z)M_(Z)O₂, and thelithium manganese composite oxide, may be selected arbitrarily, it isdesirable that these compounds are mixed together at a weight ratio of20:80 to 80:20. By setting the mixing ratio to the above range, it ispossible to realize the non-aqueous electrolyte secondary cell 1 havingoptimum cyclic characteristics and a high capacity. If the mixing ratioof the lithium nickel composite oxide and the lithium manganesecomposite oxide exceeds the above range, the cell capacity tends to belowered.

[0034] As the cathode current collector, a metal foil, such as analuminum foil, is used. As the binder, any suitable known binderroutinely used as the cathode/positive active material for this sort ofthe cell may be used. The cathode mixture may be admixed with knownadditives, such as electrically conductive materials.

[0035] The anode 3 is obtained on coating an anode mixture, containingan anode/negative active material, on an anode current collector, anddrying the anode mixture in situ to form the layer of the anode/negativeactive material on the anode current collector.

[0036] As the anode/negative active material, carbon materials, forexample, are used. As the carbon materials, those capable ofdoping/undoping lithium may be used. For example, low crystalline carbonmaterials, obtained on firing at a temperature at a lower temperaturenot higher than 2000° C., or high crystalline carbon materials, such asartificial graphite or natural graphite, and processed at an elevatedtemperature close to 3000° C., may be used. Specifically, pyrocarbon,cokes, graphite, vitreous carbon, sintered organic polymer compounds,that is furan resins sintered and carbonized at suitable temperatures,carbon fibers and activated charcoals, may be used.

[0037] For example, graphite powders of spherical, flat or fiber-likeshape, having the spacing of the (002) plane being 0.335 to 0.340 mn andthe c-axis spacing Lc being not less than 20 mn, may be used.

[0038] The anode capacity depends not only on the surface electronstructure of graphite particles, but also on its crystallinity. In thepresent embodiment, as the index for crystallinity of the graphitematerial, the spacing of the (002) crystal plane is prescribed to be notlarger than 0.3363 mn. The spacing of the (002) plane is more preferably0.3360 nm or less and most preferably 0.3358 nm or less.

[0039] In the present embodiment, in which, as an index forcrystallinity of the graphite material, the spacing of the (002) planeis prescribed to be 0.3363 mn or less, the irreversible capacity isappreciably reduced, while a high reversible capacity is obtained, inthe anode formed of this graphite material of high crystallinity.

[0040] In addition, metals or semiconductors, capable of being alloyedor of forming a compounds with lithium, may be used. Examples of metalor semiconductor elements capable of forming alloys or compounds withlithium include preferably metal or semiconductor elements of the group4B, more preferably silicon or tin, most preferably silicon. Alsopreferred are these alloys or compounds of lithium, specifically, SiB₄,SiB₆, Me₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂ Cu₅Si,FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂ or ZnSi₂.

[0041] As the anode current collector, metal foils, such as copperfoils, may be used. In the anode mixture may be contained any suitableknown binders etc. Meanwhile, the anode mixture may be admixed with anysuitable known additives as necessary.

[0042] As the separator 4, a micro-porous polypropylene film, forexample, may be used.

[0043] The cell can 5 and the cell lid 6 may be formed of, for example,iron or aluminum. If the cell can 5 and the cell lid 6 of aluminum areused, it is necessary to weld the cathode lead 8 to the cell can 5 andto connect the anode lead 9 to the terminal pin 7 to prevent reaction oflithium with aluminum.

[0044] The non-aqueous electrolyte liquid is the electrolyte saltdissolved in a non-aqueous solvent.

[0045] As the organic solvent, cyclic carbonates, such as ethylenecarbonates and propylene carbonates, non-cyclic carbonates, such asdimethyl carbonates and diethyl carbonates, cyclic esters, such asγ-butyrolactone or γvalerolactone, non-cyclic esters, such as ethylacetate or methyl propionate, and ethers, such as tetrahydrofuran or 1,2-dimethoxyethane, may be used. One of these organic solvents may beused singly, or two or more of them may be used as a mixture.

[0046] There is no particular limitation to the electrolyte salts usedprovided that these are lithium salts dissolved in organic solvents andexhibit ionic conductivity in this state. For example, LiPF₆, LiBF₄,LiClO₄, LiCF₃SO₃, LiN(CF₃SO₂)₂ or LiC(CF₃SO₂ )3 may be used. One ofthese electrolyte salts may be used singly, or two or more of them maybe used as a mixture.

[0047] As compared to the conventional non-aqueous electrolyte secondarycells containing, as the cathode/positive active materials, lithiumnickel composite oxides having a higher proportion for lithium, that isLi_(A)Ni¹⁻Z M_(Z)O₂ where A is not less than 1, the non-aqueouselectrolyte secondary cell 1, constructed as described above, is of highcapacity and improved in cyclic characteristics.

[0048] Although the non-aqueous electrolyte secondary cell 1, employinga non-aqueous liquid electrolyte, as the electrolyte, has been explainedin the foregoing, the present invention is not limited thereto, suchthat it may be applied to a non-aqueous electrolyte cell employing asolid electrolyte comprised of an electrolyte salt dissolved in a highmolecular or polymer material or a gel electrolyte in which a solutionobtained on dissolving an electrolyte salt in a non-aqueous solvent isheld in a polymer matrix, or a so-called solid electrolyte cell.

[0049] When the present invention is applied to a solid electrolytecell, the cathode and the anode are constructed similarly to the cathode2 and the anode 3 of the non-aqueous electrolyte secondary cell 1described above.

[0050] As the high molecular or polymer materials that make up the solidelectrolyte or the gel electrolyte, silicon gel, acryl gel,acrylonitrile gel, polyphosphasen modified polymer, polyethylene oxide,polypropylene oxide, and cross-linked or modified composite polymersthereof, may be used. As fluorine-based polymers, poly(vinylidenefluoride, poly(vinylidene fluoride —CO— hexafluoropropylene),poly(vinylidene fluoride —CO— tetrafluoroethylene), poly(vinylidenefluoride —CO— trifluoroethylene) and mixtures thereof may be used.

[0051] When the solid electrolyte or the gel electrolyte is used as thenon-aqueous electrolyte, a separator does not necessarily have to beprovided, since the solid electrolyte or the gel electrolyte may performthe role of the separator.

EXAMPLES

[0052] The non-aqueous electrolyte cell of the present invention willnow be explained in detail based on concrete experimental results.

Example 1

[0053] [Method for Producing Lithium Nickel Composite Oxides]

[0054] To 0.80 mol of nickel hydroxide, 0.15 mol of cobalt hydroxide and0.05 mol of aluminum atoms was added 0.90 mol of lithium hydroxide toform a mixture of a precursor of Li_(a)Ni_(0.8)CO_(0.15)Al_(0.05)O₂.This mixture was fired for five hours at 789° C. in an oxygen atmosphereto yield Li_(0.95)Ni_(0.80)CO_(0.15)Al_(0.05)O₂ as a lithium nickelcomposite oxide. This compound was checked as to its diffraction peak byan X-ray diffraction method (Cukα rays). As a result, the compound wasfound to be a compound having a diffraction peak approximatelycoincident with LiNiO₂ registered in ICPDS. The so produced lithiumnickel compound oxide was pulverized to an average particle size of 10μm. The average particle size was measured similarly by a laserdiffraction method.

[0055] [Method for Preparing Lithium Manganese Composite Oxide]

[0056] First, lithium carbonate (Li₂CO₃), manganese dioxide (MnO₂) anddichromium trioxide (Cr₂O₃) were mixed together at a preset ratio andfired in air at 850° C. for five hours to produce a manganese-containingoxide LiMn_(2−V)Cr_(y)O₄ containing lithium, manganese and a firstelement Ma (chroinum). The value of V for chromium was set to 0.15. Theso produced compound was searched by a X-ray diffraction method (X-raytube Cukα), and was found to be a compound exhibiting a diffraction peakapproximately coincident with that of a spinel type lithium manganesecomposite oxide as compared to LCPDS. The so producedmanganese-containing oxide was pulverized to an average particle size of20 μm by a laser diffraction method.

[0057] [Method for Producing a Cathode]

[0058] 37 weight parts of a lithium manganese composite oxide(LiMn_(1.85)Cr_(0.15)O₄) and 55 weight parts of lithium nickel compositeoxide (Li_(0.95)Ni_(0.80)CO_(0.15)Al_(0.05)O₂), as cathode/positiveactive material, 5 weight parts of graphite, as an electricallyconductive agent and 3 weight parts of polyvinylidene fluoride (PVDF) asa binder, were mixed together and dispersed in polyvinylidene fluoride(NMP) to form a slurried cathode mixture.

[0059] This cathode mixture was coated on both surfaces of an aluminumfoil, 20 μm thick, which is to operate as a cathode current collector.The resulting product was dried in situ and molded under compression.The resulting molded product was cut to preset size to prepare acathode.

[0060] [Method for Producing an Anode]

[0061] First, to 100 weight parts of coal-based coke, as a filler, 30weight parts of coal tar based pitch as a binder were added and mixedtogether. The resulting mixture was compression-molded by a press andheat-treated at a temperature 1000° C. or less to prepare a carbonmolded product. This carbon molded product was impregnated with coal tarbased pitch, melted at a temperature of 200° C. or less, and theresulting product was then heat-treated at a temperature 1000° C. orless. This sequence of operations was repeated several times. Theresulting product was heat-treated at 2700° C. to form a graphizedmolded product. Subsequently, the graphized molded product was crushedand classified to form powders.

[0062] The so produced graphized powders were analyzed as to structureby the X-ray diffraction method. The spacing of the (002) plane was0.337 nm and the crystallite thickness along the c-axis was 50.0 mn.Moreover, the true density as found by the picnometric method was 2.23g/cm3, the bulk density was 0.83 g/cm3, the specific surface area asfound by the BET (Brunauer Emmen Teller) method was 4.4 M²/g. As for thegrain size distribution, as found by the laser diffraction method, theaverage grain size was 31.2 μm, while the cumulative 10% grain size,cumulative 50% grain size and the cumulative 90% grain size were 12.3μm, 29.5 μm and 53.7 μm, respectively. 92 weight parts of graphite, asan anode/negative active material, and 8 weight parts of polyvinylidenefluoride (PVDF), as a binder, were mixed together and dispersed inN-methyl pyrrolidone (NMP) to prepare a slurried anode mixture.

[0063] This anode mixture was coated on both sides of a copper foil, 15μm in thickness, which is to operate as an anode current collector. Theresulting product was dried in situ and molded under compression. Theresulting molded product was cut to preset size to prepare an anode.

[0064] [Method for Preparing a Non-aqueous Liquid Electrolyte]

[0065] In a solution obtained on mixing ethylene carbonate and dimethylcarbonate at a weight ratio of 1:1, LiPF₆ as an electrolyte salt wasdissolved at a rate of 1 mol/1 to prepare a non-aqueous liquidelectrolyte.

[0066] [Method for Assembling a Cell]

[0067] The cathode and the anode, prepared as described above, werelayered together, with the interposition of a separator, 25 μm inthickness, and coiled longitudinally to prepare an elliptically-shapedcell unit.

[0068] This elliptically-shaped cell unit was inserted into asquare-shaped cell can which is 29 mm in width, 6 mm in thickness and 67mm in height. After the cell lid was welded to the opening part of thecell can, the non-aqueous liquid electrolyte was introduced via a liquidelectrolyte injection port, provided in the cell lid. The liquidelectrolyte injection port then was hermetically sealed. The abovecompleted the square-shaped non-aqueous electrolyte secondary cell.

Examples 2 to 4 Comparative Examples 1 to 3

[0069] A non-aqueous electrolyte secondary cell was prepared in the sameway as in Example 1, except that, in preparing a lithium nickelcomposite oxide, the mixing molar ratio of lithium hydroxide was set asshown in Table 1.

[0070] The initial charging was carried out on the cells of Examples 1to 4 and Comparative Examples 1 to 3, prepared as described above.First, with the constant current of 400 mA, constant current constantvoltage charging was carried out up to an upper limit voltage of 4.20 V,with the constant current being 400 mA, and constant current dischargingat 1000 mA was carried out up to the terminal voltage of 3.00 V, inorder to measure the initial voltage. Meanwhile, the initial cellcapacity used was a of a value obtained on averaging over five cells.

[0071] For the respective cells, charging for the second time and so onwere carried out for 2.5 hours, with the constant current of 1000 mA, upto the upper terminal voltage of 4.20 V. The constant currentdischarging of 1000 mA was then carried out up to the terminal voltageof 3.00 V. This charging/discharging cycle was repeated 300 times andmeasurement was made of the discharge capacity of the number 300 cycle.The ratio of the discharge capacity at the number 300 cycle to theinitial discharge capacity was found and used as a capacity upkeep ratio(unit: %). The cyclic characteristics were evaluated from the capacityupkeep ratio after 300 cycles.

[0072] The results of the above measurements are also shown in Table 1along with the mixing molar ratio (a) of lithium hydroxide in thepreparation of the lithium nickel composite oxide and the compositionsof the produced lithium nickel composite oxides. TABLE 1 initialdischarge volume upkeep LiOH ratio lithium nickel composite oxidescapacity (mAh) ratio (%) Ex.1 0.95Li_(0.95)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 893 92 Ex.2 0.97Li_(0.97)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 963 90 Ex.3 0.99Li_(0.99)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 970 91 Ex.4 0.995Li_(0.995)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 975 90 Comp. Ex.1 0.9Li_(0.9)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 721 91 Comp. Ex.2 1Li_(1.00)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 980 73 Comp. Ex.2 1.02Li_(1.02)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ 979 70

[0073] As may be seen from Table 1 that, in the Comparative Example 1containing the lithium nickel composite oxide where a is less than 0.95,the lithium content in the cathode/positive active material is small,the cell is not sufficient in capacity and hence is inappropriate as autility cell. On the other hand, with the Comparative Examples 2 and 3containing the lithium nickel composite oxide with a not less than 1,the initial cell capacity is that high, however, the cycliccharacteristics of the cells are lowered.

[0074] It is also seen from Table 1 that the samples 2 to 5 containinglithium nickel composite oxides where 0.95≦a<1 are larger in cellcapacity and undergo only little cyclic deterioration. It is also seenthat the samples 3 to 5 containing lithium nickel composite oxides, with0.97≦a≦0.995, are superior in cyclic characteristics, with the initialcell capacity exceeding 900 mAh, such that these cells are particularlydesirable as utility cells.

[0075] Thus, it may be seen that the non-aqueous liquid electrolytesecondary cell, containing a lithium nickel composite oxide as thecathode/positive active material, with a being such that 0.95≦a<1, issuperior in cyclic characteristics and is of a high capacity.

[0076] In Examples 5 to 10, plural cells were prepared as the firstelement Ma of the lithium manganese containing composite oxide waschanged, and high-temperature storage characteristics of the so producedcells were searched. In Examples 11 to 16, plural cells were prepared asthe second element Mb of the lithium manganese containing compositeoxide was changed and high-temperature storage characteristics andcyclic characteristics of the so produced cells were searched.

Examples 5 to 10

[0077] Plural cathodes were prepared in the same way as in Example 1,except preparing a manganese-containing oxide as the first element (Ma)was changed as shown in the Table 2 shown below in the preparation ofthe lithium-manganese containing composite oxide, and plural non-aqueousliquid electrolyte secondary cells were prepared.

[0078] Meanwhile, in preparing the lithium-manganese containingcomposite oxide, cobalt monoxide and dialuminum trioxide (Al₂O₃) wereused in Examples 5 and 6, respectively, in place of dichromium trioxideof Example 1, while magnesium monoxide (MgO) and zinc monoxide (ZnO)were used in Examples 7 and 8, respectively, in place of dichromiumtrioxide of Example 1. Similarly, tin monoxide (SnO) was used in Example9, in place of dichromium trioxide of Example 1, while cobalt oxide anddichromium trioxide were used in Example 10 in place of dichromiumtrioxide of Example 1.

Examples 11 to 16

[0079] Plural cathodes were prepared in the same way as in Example 1,except preparing a lithium-nickel containing oxide as the second element(Mb) was changed as shown in the Table 2 shown below in the preparationof the lithium-nickel containing composite oxide, and plural non-aqueousliquid electrolyte secondary cells were prepared.

[0080] Meanwhile, in preparing the lithium-nickel containing compositeoxide, diiron trioxide (Fe203) and dialuminum trioxide were used inExamples 11 and 12, respectively, in place of cobalt hydroxide andtrialuminum trioxide of Example 1. Similarly, magnesium oxide and zincoxide were used in Examples 13 and 14, respectively, in place of cobalthydroxide and trialuminum trioxide of Example 1. On the other hand, tinmonoxide was used in Example 15 and cobalt monoxide and dialuminumtrioxide were used in Example 16 in place of cobalt hydroxide andtrialuminum trioxide of Example 1.

[0081] Of the cells of the Examples 5 to 10, 11 to 16 and the Example 3,prepared as described above, high temperature storage characteristicswere scrutinized. As the high temperature storage characteristics, ageneral discharge capacity upkeep ratio under general dischargeconditions on storage at elevated temperatures and the high loaddischarge energy under high load discharge conditions were found.

[0082] Meanwhile, the general discharge capacity upkeep ratio followingstorage at elevated temperatures was found as follows: First,charging/discharging was carried out in a constant temperature vesselmaintained at 23° C. to find the initial discharging capacity. It isnoted that charging was carried out at a constant current of 1A untilthe cell voltage reached 4.2V, and subsequently was continued at aconstant voltage of 4.2V until the sum total of the discharging timeequaled to three hours. The cell was then discharged at a constantcurrent of 0.5 A until the terminal voltage (cut-off voltage) of 3.0 Vwas reached. This was set as the general charging/discharge condition.

[0083] The cell then was charged again under this general chargingcondition and stored for two weeks in an oven maintained at 60° C. Thecell then was discharged in a constant temperature vessel of 23° C. onceto a terminal voltage of 3.0 V. Ten cycles of the charging/dischargethen were carried out under the general charging/discharge condition andthe value which was maximum during these ten cycles was adopted as thedischarge capacity following storage at the elevated temperatures, andthe ratio thereof to the initial discharge capacity was adopted as thegeneral discharge capacity upkeep ratio following storage at elevatedtemperatures.

[0084] The cell was stored at 60° C. for two weeks and discharged onceto a terminal voltage of 3.0Vin the constant temperature vessel of 23°C., after which the cell was charged at a constant current of 1.5 A tothe terminal voltage of 3.0V and subsequently discharged under a highload. From the results of this discharge under a high load, the highload discharge energy following storage at elevated temperatures wasfound.

[0085] As for the charging/discharge cycle characteristics at ambienttemperature, 200 cycles of charging/discharge cycle characteristics werecarried out under the aforementioned general charging/dischargeconditions, in the constant temperature vessel maintained at 23° C., andthe ratio of the discharge capacity of the number 200 cycle to thedischarge capacity of the number two cycle (capacity upkeep ratio) wasfound.

[0086] The results of evaluation of high temperature storagecharacteristics and charging/discharge characteristics at ambienttemperature and charging/discharge cyclic characteristics at ambienttemperature of the cells of Examples 5 to 16 and the Example 3 are shownin Table 2 along with the values of the first element (Ma) of themanganese-containing composite oxide and the values of the secondelement (Mb) of the lithium nickel composite oxide: TABLE 2 volumeupkeep ratio following storage at discharge capacity volume upkeepelevated temperature following storage ratio following first element Masecond element Mb (%) (Wh) 200 cycles (%) Ex. 3 Cr0.15 Co0.15Al0.15 902.98 94 Ex. 5 Co0.15 Co0.15Al0.15 91 2.95 95 Ex. 6 Al0.15 Co0.15Al0.1590 2.93 94 Ex. 7 Mg0.15 Co0.15Al0.15 92 2.95 93 Ex. 8 Zn0.15Co0.15Al0.15 90 3 94 Ex. 9 Sn0.15 Co0.15Al0.15 91 2.96 93 Ex. 10Co0.1Cr0.1 Co0.15Al0.15 91 2.95 93 Ex. 11 Cr0.15 Fe0.20 90 2.95 92 Ex.12 Cr0.15 Al0.20 92 2.97 92 Ex. 13 Cr0.15 Mg0.20 92 2.97 93 Ex. 14Cr0.15 Zn0.20 91 2.97 93 Ex. 15 Cr0.15 Sn0.20 90 2.96 94 Ex. 16 Cr0.15Co0.25Al0.05 91 2.94 94

[0087] As may be seen from Table 2, the general discharge capacityupkeep ratio following storage at elevated temperatures and the highload discharge energy following storage at elevated temperatures were90% and not less than 90 Wh, which were higher values as in Example 3.In addition, satisfactory results could be obtained forcharging/discharge characteristics at ambient temperatures.Specifically, it was seen that superior high temperature storagecharacteristics as those in Example 3 could be obtained with use of amanganese-containing oxide in which the first element is changed to anelement other than chromium or with use of a lithium nickel compositeoxide in which the second element is changed to an element other thancobalt.

[0088] In Examples 17 to 20 and in Comparative Examples 4 and 5, pluralcells were prepared as the mixing ratio of the lithium-manganesecontaining composite oxide and the lithium-nickel containing compositeoxide was varied and the high temperature storage characteristics aswell as cyclic characteristics of the so produced cells were evaluated.

[0089] Plural cathodes were prepared in the same way as in Example 1except changing the mixing ratio of the lithium-manganese containingcomposite oxide and the lithium-nickel containing composite oxide asshown in Table 3, and non-aqueous liquid electrolyte secondary cellswere prepared using these cathodes.

[0090] Meanwhile, in Example 21, the mixing ratio of thelithium-manganese containing composite oxide was lowered, whereas, inExample 22, the mixing ratio of the lithium-nickel containing compositeoxide was lowered.

[0091] Of the cells of Examples 17 to 22, produced as described above,the high temperature storage characteristics and charging/dischargecharacteristics at ambient temperature were searched in the same way asin the above-described evaluation method. The results of the evaluationare shown in Table 3, along with the value of the first element ma ofthe lithium-manganese containing composite oxide and the value of thesecond element Mb of the lithium-manganese containing composite oxide:TABLE 3 volume upkeep ratio discharge following storage at capacityvolume upkeep mixing ratio (weight parts) elevated temperature followingratio following 200 LiMn1.85Cr0.15O4 Li0.99Ni0.8Co0.15Al0.05O2 (%)storage (Wh) cycles (%) Ex. 3 40 60 90 2.98 94 Ex. 17 20 80 92 2.9 92Ex. 18 50 50 90 3 95 Ex. 19 60 40 89 3.05 93 Ex. 20 80 20 88 3.1 94 Ex.22 10 90 92 2.7 90 Ex. 23 90 10 84 2.8 90

[0092] As may be seen from Table 3, the higher the mixing ratio of thelithium-manganese containing composite oxide, the larger is the highload discharge energy following storage at elevated temperature,whereas, the higher the mixing ratio of the lithium-nickel containingcomposite oxide, the higher is the general discharge capacity upkeepratio following storage at elevated temperature. In particular, theExamples 3 and 17 to 20 are seen to be excellent both in the dischargecapacity upkeep ratio following storage at elevated temperatures and inthe high load discharge energy following storage at elevatedtemperature, which are 88% or higher and 2.90 Wh or higher,respectively.

[0093] Conversely, with Example 21 with the low mixing ratio of thelithium-manganese composite oxide, the high load discharge energyfollowing storage at elevated temperature is small, whereas, withExample 22 where the mixing ratio of the lithium-nickel composite oxideis low, the capacity upkeep ratio following storage at elevatedtemperature was low.

[0094] That is, by setting the mixing ratio of the lithium-manganesecomposite oxide and the lithium-nickel composite oxide so that thecontent of the lithium-nickel composite oxide is 80 to 20 to the contentof the lithium-manganese composite oxide of 20 to 80, particularlyexcellent high temperature storage characteristics can be achieved.Meanwhile, excellent results could be obtained as to thecharging/discharge characteristics at ambient temperatures.

What is claimed is:
 1. A cathode/positive active material containing alithium nickel composite oxide represented by the general formulaLi_(A)Ni_(1−Z)M_(Z)O₂, where A is such that 0.95≦A<1, Z is such that0.01≦Z<0.5 and M is at least one of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga,Cr, V, Ti, Mg, Ca and Sr.
 2. The cathode/positive active materialaccording to claim 1 wherein A of the general formula is such that0.97≦A<0.995.
 3. The cathode/positive active material according to claim1 containing a lithium manganese composite oxide.
 4. Thecathode/positive active material according to claim 3 wherein saidlithium manganese composite oxide is a compound represented by thegeneral formula Li_(X)Mn_(2−Y)M′_(Y)O₄, where X is such that 0.9≦X, Y issuch that 0.01≦Y≦0.5 and M′ is at least one of Fe, Co, Ni, Cu, Zn, Al,Sn, Cr, V, Ti, Mg, Ca and Sr.
 5. The cathode/positive active materialaccording to claim 3 wherein the lithium nickel composite oxiderepresented by the general formula Li_(A)Ni_(1−Z)M_(Z)O₂ and the lithiummanganese composite oxide are mixed at a weight ratio of 20:80 to 80:20.6. A non-aqueous electrolyte cell including a cathode containing acathode/positive active material, an anode containing an anode/negativeactive material and a non-aqueous electrolyte wherein thecathode/positive active material contains a lithium nickel compositeoxide represented by the general formula Li_(A)Ni_(1−Z)M_(Z)O₂, where Ais such that 0.95≦A<1, Z is such that 0.01≦Z≦0.5 and M is at least oneof Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca and Sr.
 7. Thenon-aqueous electrolyte cell according to claim 6 wherein A of thegeneral formula is such that 0.97≦A≦0.995.
 8. The non-aqueouselectrolyte cell according to claim 6 containing a lithium manganesecomposite oxide as said cathode/positive active material.
 9. Thenon-aqueous electrolyte secondary cell according to claim 8 wherein saidsaid lithium manganese composite oxide is a compound represented by thegeneral formula Li_(X)Mn_(2−Y)M′_(Y)O₄, where X is such that 0.01≦X, Yis such that 0.01≦Y≦0.5 and M′ is at least one of Fe, Co, Ni, Cu, Zn,Al, Sn, Cr, V, Ti, Mg, Ca and Sr.
 10. The non-aqueous electrolytesecondary cell according to claim 8 wherein the lithium nickel compositeoxide represented by the general formula Li_(A)Ni_(1−Z)M_(Z)O₂ and thelithium manganese composite oxide are mixed at a weight ratio of 20:80to 80:20.
 11. The non-aqueous electrolyte secondary cell according toclaim 6 wherein said anode uses, as an active material, one or morecarbonaceous materials capable of doping and undoping lithium and whichare selected from the group consisting of pyrocarbon, cokes, graphite,vitreous carbon, sintered organic high molecular or polymer compounds,carbon fibers and activated charcoal.
 12. The non-aqueous electrolytesecondary cell according to claim 6 wherein said anode is formed byspherical, flat or fiber-like graphite powders having the spacing of the(002) plane being 0.335 to 0.340 nm and the c-axis spacing Lc being notless than 20 nm.
 13. The non-aqueous electrolyte secondary cellaccording to claim 6 wherein said cathode is formed by a currentcollector on each side of which is coated a layer of a mixturecontaining an active material, said anode is formed by a currentcollector on each side of which is coated a layer of a mixturecontaining an active material, said cathode and the anode beinglaminated together via a separator in-between to form a laminatedproduct which then is spirally wound about itself a number of times toform an electrode unit.